The proposed research addresses the capacity for plasticity and recovery of the central connections of the chorda tympani (CT) nerve within the nucleus of the solitary tract (NST) of the adult rat. In the adult rodent the peripheral gustatory system is capable of regeneration and substantial functional recovery following deafferentation. However, very little is known about the central consequences of peripheral gustatory system damage in the mature animal. During early development, damage to the taste receptors produces significant structural and functional abnormalities in the NST. How is the gustatory there permanent alterations as seen during development? The goal of the proposed research is to examine the physiological and anatomical effects of peripheral deafferentation and regeneration and factors that influence central neural plasticity in the adult rat. In each study, the neurophysiological response properties of single NST neurons will be characterized following stimulation of peripheral determined, and the terminal field of regenerated CT axons will be assessed using HRP histochemistry. The proposed project has three specific aims: (1) TO investigate the NST following peripheral deafferentation and regeneration of the CT nerve. experiments test the hypothesis that regenerating CT axons re-establish normal terminal fields and make normal functional connections within the NST; (2) To investigate neural factors that influence the plasticity of the CT-NST connections following peripheral denervation and regeneration. Experiments test the hypothesis that the anatomical distribution and functional connections of intact and regenerating CT taste fibers in the NST (a) are influenced by those of other gustatory nerves and (b) differ in their ability to exhibit plasticity; and (3) To investigate receptor factors that influence the plasticity of the CT-NST connections. Experiments test the hypothesis that the terminal field and functional connections established by the regenerating Ct are influenced by (a) the receptor field it innervates-- anterior tongue or posterior tongue, and (b) the sodium sensitivity of the anterior tongue in animals fed low-salt diets, as seen during development.